Telephone system



Nov. 30, 1937. w. G. PATTERSON ET A1. 2,100,515

TELEPHONE SYSTEM Filed Nov. 9, 1955 8 sheets-sheet 1 Nov. 30, 1937. w..@..PATTl-:RSQN ET'AL- j 2,100,515

TELEPHONE SYSTEM Filed Nov. 9, 1955 8 Sheets-Sheet 2 ..7 ma MQ. m n um,.www www M .www x J 1 mw .ww 3E .R6 1+. N3, J. J @n mm. J J

ma Qw .usml 83% H Nov. 30, 1937. w. G. PATTERSON ET Al. 2,100,515

TELEPHONE SYSTEM Filed Nov. 9, 1935 8 Sheets-sheet 5v Nov. 3G, 1937. w.G. PATTERsoNEr Al. 2,100,515

TELEPHONE SYSTEM Filed. Nov. 9, 1935 8 Sheets-Sheet 4 Nov. 30, 1937. w.G. PATTERSON ET ALy u 2,100,515

TELEPHONE SYSTEM Filed Nov. 9, 1935 8 sheets-sheet 5 Nov 30, 1937. w. G.PATTERSON Er A1.

TELEPHONE SYSTEM Filed NOV. 9, 1955 8 Sheets-Sheet 6 Rack@ juk Wm MM,96e Herne/Ps oN Nov. 30, 1937. l w. G. PATTERSON ET AL 2,100,515

TELEPHONE SYSTEM Filed Nov. 9, 1935 sheets-sheet 7.

,if #s x Ffa/21 N0V- 30, 1937- W. G. PATTERSON ET A1. 2,100,515

TELEPHONE SYSTEM 8 sheets-sheet 8 Filed NOV. 9, 1935 .wahl

fia/Mun rrr:

Patented Nov. 30, 1937 UNITED STATES PATENT OFFICE TELEPHONE SYSTEMWilliam George Patterson, Mottingham, London, and Reginald Griith Dixon,Eltham, London, England, assignors to Siemens Brothers 8aV CompanyLimited, London, England Application November 9, 1935, Serial No. 48,952In Great Britain November 14, 1934 3 claims.

` switches employed in a connection are held under the control of thecaller but systems are known in which the release of a connection andthe freeing of the line circuits of both subscribers engaged in aconnection is effected only after both subscribers have cleared. In asystem of this latter type the calling subscribers line circuit is heldengaged unnecessarily should the called subscriber delay clearing.

In the present invention arrangements are provided for maintaining theroute over a train of switches employed in a connection until bothsubscribers have cleared yet allowing that subscriber who has cleared tomake and receive calls during the time the route is held by the othersubscriber. The arrangements are especially applicable to a system inwhich a calling line is connected to' common switching apparatus bymeans of. a call nder.

In the arrangements of the invention a signal is transmitted from thepoint at which the control of a connection is situated, i. e. a feedingbridge circuit, when, after a communication between the two parties to acall has been established, one of. them clears, the effect of the signalbeing to place an engaged marking on all the switches employed in theconnection and to prevent their release yet effect the removal of theengaged marking of and the release of the cut off relay in the linecircuit of the rst party to clear. If the switches to be held arenon-homing switches the signal has only to bring about the aforesaidengaged marking, the ordinary releasing arrangements operating as usual.If any of the switches over which a connection is established are homingswitches the signal must provide for maintaining the switch wipers onthe contacts on which they were last used yet allow i'or the release cithe cleared subscribers cut-off relay and the removal of the engagedmarking.

The invention may be applied to a full automatic system or to asemi-automatic system. The invention will be regarded, in the followingspeciication as applied to a system in which a calling line isautomatically extended to a cord circuit at an operators position and tothe operators telephone, and in which the operator upon ascertaining thesubscribers requirement further extends the connection by inserting thecord circuit to which the calling line was extended into the jack of thevwanted line, leaving the apparatus automatically to complete or torefuse to complete the connection in accordance with the` free orengaged condition of the wanted line. Clearing of an establishedconnection is effectedl by theoperator in response to a doublesupervisory signal, though either subscribers line is freed for furtheruse, either for the initiation or receipt of calls, as soon as thesubscriber hangs up his telephone.

General 10 The system in connection with which the invention will bedescribed is one in which subscribers lines are served incommon by anumber of cord circuits to which they gain 'access by 'way of linefinders and in which the line iinder which is to be set into operationin response to a call, and consequently the cord circuit to which acalling line is to be extended, is allotted by an allotter whichperforms its allotting function in response to a start signaltransmitted, to it by the said calling line.

Moreover, in the system in connection with which the invention will-bedescribed, it will be supposed that the subscribers lines are dividedinto groups of. twohundred lines and that, for the service of each suchgroup, there is assigned a suitable number of line-finders andcord-circuits, and two hundred lines of a group appearing, in multiple,in the banks of all the line-nders assigned thereto. It may be assumedthat there are eight hundred subscribers lines; consequently, there willbe four groups of subscribers lines and these four groups will be servedbyfour groups of line-finders.

Still further, it will be supposed that there is, associated with eachgroup of two hundred subscribers lines and its associated group oflinenders, one allotter which deals, primarily with calls initiated bysubscribers in its own group, allotting for use in connection therewithone of the associated `line-iinders, .but which may be borrowed by othergroups of` lines in order that it may deal, seconda-lily, with callsinitiated byY a subscriber in such other groups of lines and may 45allot, for use in connection with such calls, linefinders associated,not with the group of subscribers lines which it primarily serves, butassociated with the group by which it is borrowed. Such borrowing of anallotter which primarily serves one group of two hundred lines by a lineof another group occurs when the allotter which should, as its primaryduty, serve the said other group of lines is either already occupied inallotting a line-finder or has been put out of service on account ofsome derangement.

Since an allotter has to be able to allot any rline-lnder, according tothe circumstances of a call, in any one of four groups of such, it isapparent that the service wires between the allotters andtheline-finders must be multipled over the banks ofA all the allotters.From this it is apparent that when a calling line demands r the servicesof an allotter, whether of that which primarily serves it or of onewhich serves it as its secondary, tertiary, or quaternary duty, suchcalling line must, in order thatthe allotter shall groups of two hundredlines, that is, there appear Y in their banks the contacts of twohundred lines'. The line-iinders are of that type in which the wipersoccupy one position for'either of twoV lines and 'selection oi one orother ofv the two lines is eiected by a selection of one or other of twosietsof wipers, one ofwhich is in association with Y the contacts of oneof the two lines and the other 0f which Vis in association Ywith thecontacts of the other of the twoV lines. From this it is apparent thatwhen a calling line demandsth-eservices of an allotter, it is necessarythat the calling'line inform the allotter to Ywhich of the twosub-groups of one hundred lines, which constitute a group' of twohundredl lines, such calling line belongs in' order that the: allottermay select Y the correct set of' wipers of such line-finder as it `othergroups to its initial position;

may. allot.

Take Vfo'r consideration any group of line-iind-r ers; theline-nders ofthis group are, in the system under description, divided into twovsubgroups which may be designatedl respectively directlyconn'ecte'dline-finders and indirectly connectedline-nders; The directly connectedlinefinders terminate directly in cord-circuits; the indirectlyconnected line-findersl terminate inthe banks of` secondary line-ndersover which, indirectly, they reach cord' circuits.

An allotter;v in" allotting aline-finder of the group inv questionalways allots a directly connected" line-finder if thereris oneavailableand allots an indirectly connected one only if thereV i s nodirectlyrconnected' one available. The service wires of' the directlyconnected line-iindersY are therefore'connected to the bank-of theallotter in advance ofY those of the indirectly connected line-finders.The allotters are; however, switches which do not necessarily return,after use, to an initial position but which under certain conditionspreselect', after use in connection with'A one call, anY idleline-finder, for use in a subsequent call or, under' other conditionsreturn to ari-initial position; Thus, ifv an allotter has been usedinthe operationof allottinga directlyconnectedV line-lnder. inr oneVgroup of such, it, uponrelease, preselects another idle line-finder inthe; same group, if such exists, ready for use in a subsequent call. I-fsuch idle line nder does not eXist-thefallotter passes through thepositions occupied byindirectly connected line-inders iof the samegroupand also, if such should lie in its path, through the positionsoccupied by both directly and indirectly connected line-finders of g Iftheallotter has been used' in the operation :of allotting an indirectlyconnected' line-iinder it, upon release; invariably-passes throughA allintervening positions to its initialV position. Further, it. may

very well happen that when an allotter is taken into use there may beavailable no directly connected line-iinders between the position inwhich its wipers are standing at the time the demand occurs and that inwhich the first indirectly con- Y nectedV line-finder-appears; -It istherefore arranged that, before an allotter,'which has started from someintermediate position, can allot an Aindirectly connected line-nder, itmust pass through its initial position in order that it may havean'opportunity of allotting a directly con- Y nected line-iinderif suchshould be available.

It may be noted that, for night service, the allotter always allotsindirectly connected lineinders: this is within the general statementmade :above for at night the directly connected linei'lnders arerendered unavailable by reason of the positions, upon which are situatedthe cord circuits inl which they terminate, being unstaffed.

Still in the system in connection with which the Vinvention is beingdescribed, the indirectly connected line-finders areterminated, as hasbeen stated,` in the banks of secondary line-finders. Although theindirectly connected line-finders are the residue as it were, of fourgroups of linenders serving `four groups of two hundred lines, thesecondary line-iinders are divided'into two groups and each group serveshalf of the indirectly connected line-finders. `The indirectly connectedline nders'may therefore be regarded as re-grouped into two groups and,in what follows, will be so regarded; the four fold grouping being nowconveniently ignored.

A group of indirectly connected line iinders is served by a group ofsecondary line i'lnders in the banks of which the indirectly connectedline iinders are connected in multiple.

It will be supposed that there is associated with each group ofsecondary line finders one secondary allotter which deals primarily withcalls extended over an indirectly connected line finder torthat groupYof secondary .line-iinders with whichY the allotter under considerationis f associated, allotting for use in connectionV with such extendedconnection a secondary line iinder which it primarilyjserves. y Y everthat the secondary allotter associated with the group of secondary linefinders under oonsideration may be borrowed by the other groupY ofsecondary line finders, which it may then 'serve as its secondaryduty,allotting for use in a connection extended to said other group ofsecondary line-finders a secondary line-finder `of such secondarilyserved group of secondary linenders. Y

In addition to the two secondary allotters each of which is, as alreadystated, associated, for

It is 'arrangedhowprimary duty, with one of the-group of secondaryline-nders and each of Vwhich is borrowable, for secondary duty, by theothergroup of secondary line-iinders, there is provided'a third (or asit may preferably be called additional) secondaryV line-lnder the dutyof which is to serve either of the groups of secondary line-finders'whentwo calls are made at the same time in one group of g indirectlyconnectedline-nders. By this means ary allotter be informed from whichgroup of indirectly connected line-finders the call comes in order thatit may be able to allot a secondary line-finder of that group which itprimarily serves or of that group which it secondarily serves. It isnecessary to give similar information .to the additional allotter.

Unlike. the directly connected line-finders which, it will be recalled,terminate directly in cord circuits, the secondary line-findersterminate in the wipers of cord-seekers to the banks of which areconnected cord-circuits and calling circuits, the latter of whichterminate upon a night operators position. The cord seekers are causedto select, according to circumstances, a cord circuit or a callingcircuit on the night operators position by means of a wiper switchingoperation.

Apparatus `acting type, the banks of which accommodate fifty-twocontacts. To set one of these motordriven switches into operation, alatch magnet'I withdraws a latch from a toothed wheel and closes acircuit for the motor magnet. To stop such a switch the latch magnetopens the motor circuit and re-applies the latch. The motor and latchwill not be shown in the drawings.

In the primary line-nders, the wipers are connected together in pairs,the two of a pair are angularly displaced to the extent of and one wiperof a pair operates over one levelV whilst the other wiper of the samepair operates over another level of a bank. `As one wiper of a pairleaves its level the other enters its level. Thus by one completerevolution of the switch a pair of wipers serves the contacts of onehundred lines. There are as many such pairs as may be necessary.

Since the directly and indirectly connected linefinders serve twohundred lines, the wipers and banks are duplicated and one pair or theother pair of two pairs of wipers is selectable by means of a switchingrelay. Thus either the pair of wipers which serves, say the positive,level of one hundred lines or the pair of wipers which serves the likebanks of the other hundred lines may be connected by the switching relayto the positive conductor of the cord, and similarly for the negativeand other levels.

In the diagrams one of the wipers of a pair in the line finders and thearc (representative of a level of fty-two contacts) which it serves areshown in full and the other in dotted lines.

In the allotters and cord-seekers, the wipers are connected together inpairs, the two wipers of a pair are angularly displaced to the extent of180, and the wipers of a pair operate successively over the same level.Thus one complete revolution of such' a switch serves fty-two contactstwice.

As the number of circuits which aprimary allotter can serve is more thancan be served over one set of levels the levels (and their pairs ofwipers) are duplicated and wiper-switching is provided. This must not beconfused with the wiper-switching at the primary line-nders.

As the cord-seekers have to serve cord-circuits one sort being servedover one set of wipers and levels,.and circuits of the other sort beingserved over the other set of wipers and levels and wiperswitching beingprovided. Y

Circuits,A general It is now possible to refer to the accompanyingcircuit diagrams, and certain' features thereof will be referred tobefore a detailed description ofthe operation is given.

Apair of start wires Iwa: and lyz one appropriate to one sub-group ofone hundred lines and the other to the other sub-group of one hundredlines of a group of two hundred lines, extends lto a primary start relaygroup Fig. 2. Other pairs of start wires 21.0.7: and Zyz, Swix and Syzand 410x and Aya extend from the two sub-groups of the remaining groupsof two hundred lines.

In the primary start relay group are four pairs of relays SA and SB, SCand SD, SE and SF, SG and SI-I. Each pair of relays is associated withand controlled by one of the primary allotters in such manner that ifthe primary allotter is available the associated pair of relays isoperated. For the sake of simplicity only one of the allotters, one ofthe pairs of relays SA and SB, and the circuits which this pair ofrelays control and by which they are controlled, are fully shown: theothers are similarly arranged.

A primary allotter, Figs. 3 to 6, includes a group of relays A to I-l,Fig. 3, which control a marker, Fig. 4, in such manner as to inform theallotter in which group of two hundred lines a calling line is situated.These relays also control a rrelay AB, Fig. 6, in such manner as toinform the allotter in which sub-group of one hundred linesY a callingline is situated. The marker also serves to inform the allotter if it isserving in a primary,

secondary, tertiary, or quaternary capacity and whether it is to allot adirectly or indirectly connected line-finder. These points will beunderstood later.

`wiper switching at the indirectly connected line- .iinder and to thatgroup of two hundred lines which the primary aliotter serves in itsquaternary capacity. Allotter number 2 (associated with relays SC andSD) should serve the caller as its primary duty but it is supposed to beunavailable, as are allotter 3 (relays SE and SF) which should as itssecondary duty, and allotter number 4 (relays SG .and SH) which shouldas its tertiary duty, serve the calling line. This will involve thesupposition that the pairs cf relays SC and SD, SE and SF, SG and SH arereleased and that the pair of relays SA and SB are operated (theallotter shown in Figs. 3 to 6 being available). The

fill

starting Awires appropriate to the group of linesA to which that chosenfor the purpose of description-belongs are. 211m: and Eye and thatappropriate to the sub-group is Eye.'

The example chosen forv description will bring into operation themaximum of apparatus. Di-

kgressions will be'made to show whatwould have happened .un-der @othercircumstances.

iThe dirgressions may ,be passed by if desired: `they willberecognizedby afsuitable introduction and each :will be con'ned withina single paragraph, -enclosed .within brackets.

When the subscriber, vwhoseexchange equipment is shown in Fig. 1,initiates a call, a loop is closed for his line relayLS. `Relay LSoperates.

'Relay LS qt `cfmtacts-lsI connects negative by way of resistance RS'towire ps, ls2 'disconnects `onesource of. earth from Wire +s-,Zs3performs an operation which has no present interest, ls4 dis- :connectsnegative from wirepm Vin the calling -subscribers .multiple to renderthe line unavailable as a called line, Land ls connectsearth to wirelye.A'Ihisfearth extends by way of contacts d2 (Fig. 2), similar contacts(indicated `by .'L) of the otherallotters, sed, sed, 8g4 andsa, to relayD, (Fig.i.3). .Relay D operates.

Relay -D at its-contacts.-d| closes a holding circuit for itself wherebyit is rendered independentof -any change inthe availability of otherallotters,`d2 open'sits own original operating circuit sothat no otherline in the same sub-group "can,iforthe5moment, obtain the services-ofan allotter, d3 closes an alternative holding circuit so that relay Dmay not ybe released until the allotter is available for service, d4disconnects negative from vthe so-called normal contact in bankAPl ofthe-line-ndershown and of all those of the same group so that'such a oneas may be eventually set intooperation may pass through normal ifnecessary, d5 (Fig-6) Acloses a circuit forwinding AA(I) of relay AA,and d6 (Fig. 4) prepares a point in marking Wire l0. Relay AA operates.

Relay AA'at incomoda-aal performs'anop- Veration Which-has no presentinterest, cm2 closes a circuit for 'relays AC 'and AD, aa3 prepares acircuit for Winding JA(I) of"relay VJA. j

Here it may be interposed that if relays A or C had been operated-due tothe allotter beingV called on for primary duty-contacts a5 or c5 wouldhave closed a circuit for winding AB(I) of relay AB. Relay AB would haveoperated and have at contact aM removed a short circuit from VwindingAA(II) of relay AA,'at contact abl prepared a holding circuit forWinding AB(III) of relay AB, and at contacts c1125 and ab6 modied the'marken Relays AY and Calso would'have suitably modified the marker.Contact aal would have substantiated contact abd. If relay B had beenoperated-allotter performing quaternary duty for the sub-group otherthan that to which the caller shown belongs-contacts of relay VBwouldhave had the same effect Yas those of relay D except that themarker would have been differentlyoperated.` If vrelays E or G had beenoperated-allotter performing tertiary dutycontacts `e5 or U6 would haveclosed a circuit for winding AB(II) of relay AB. Relay AB would haveoperated and would have, at contact ab3 closed a circuit for WindingJA(II) of relay JA. Relay AA would 'not have been operated; thereforerelays AC and AD would not have been operated and the allotter wouldwork over its even numbered levels. If relays F or I-I had beenoperated-allotter performing secondary duty-re-V lay JA would have beenoperated without'relays AA, AB, AC or AD being operated. The allotterwould then have worked over itseven numbered levels.` 'Y Y Rezays'Ac and.4D @when contacta-acl to ac'5 and adl nto ad3 switch outtheevennumbered wipers and switch in the odd numbered wipers of v thezallottersince it :.is ."overthesewipers 1 that ,the allotter i. is able tozserve i those line-flnders which serve'the group lof calling linesto'which the'call- Y zinglineshownfbelongs, acB and ad5 close the al-.ready prepared'circuit for winding JA(I) of relay JA, and add (Fig. `4)divert the marking circuit from those wires which maybe served by wipertltovthose which may beserved by wiper' li5.

Relay JA atts contacta-:iai (Fig. 5) closes a icircuitLforwindingKAG) ofrelay KA, 7'a2 (Fig. r3) prepares a circuitfor relay'TA, i113 opens thevcircuitfonrelays SAV and SB to guard the allotter yfromin'trusion by`other calling lines, jail opens a .point in the circuitof windingKA(II) of relay KA .toallow theallotter topass throughnormal Eifnecessaryin the course ofthe search for an idle linender,;and Yjailcompletes the marking circuit for wire I0, which wire will be supposedto be connected in multiple to the rst group of contacts in the firsthalf ofbank l5 and to be appropriate lto those directly connectedlinevvilndersthat are fable vto serve the group of subscribers linestowhich the caller belongs. Relay KA operates. Y

`Relay KA atz'ts contacta-kal closes a holding circuit for itself, tov atiming contact e, lca2 closes a circuit for latch `4magnet MUA (fromearth via contacts Zal, malglcaZ, qa4, ael, magnet MUA, to negative),ka3 substantiates contact 7a3, 7ca4 closes a1 circuit' for relay TAwhich relay however, is short circuited in all positions of thefallotterexceptits-normal position, which position, for the .present'it willbesupposednot to be occupying,

Vlcai'prepa'res .a circuit, at present short circuited `bycontactlal andmal forxrelays'MA andzNA, 'andka closes ia pointin'the circuit :ofwinding KA(II) of relay/KAfor apurpose which will be -referred l,tolater. Latch` magnet MUA 'energizea (Latch Imagnet MUA, when energized,serves to Withdrawa latch from the motor (not shown) of "the 'allotterand `to completeV the circuit of that motoriand, When deenergized, toopenV the cir- :cuitiof and Ato relatch themotor.)

Under 'our present supposition, that there are `no idle directlyconnected line-linders in the lgroup, marked overwire Il), which canserve the caller,ithe'allotter will be required to allot an .indirectlyconnected one. It will therefore rotate Yits wipers, which may besupposed to `be standing at a position about half way through thosewhich :are-associated :with andmarked by wire llypast allthe'intervening directly connected line1indV ers, :pastthe indirectlyconnected line-finders of :the samegroun'past the next group of directlyvand indirectly connected line-finders (namely `those which in bankl5'are adapted to be marked over WiresQ and i8) to normal. The wiperswill rotate past these contacts because wires I9,v9 and 18 :are notmarked. It Vwill be seen that, although an indirectly connectedline-finder is Wanted, the allotter has ignored them and has gone tonormal. This is in order that the allotter may-ascertain thatthosedirectly connected linenders which lay behind the 'position in which theallotter stood when called on `for service were actually notiidle. Theallotter obviously ignored the directlyand indirectly connectedline-finders` which it serves in the second half of'itslevel l5V becausesuch liner-finders are incapable of serving the group of lines 'to whichthe caller belongs.

As the'allottervpasses through its normal position it opens itsvoff-normal contacts ON (Fig. 3) thereby removing the short circuit fromrelay TA. Relay TA-which isa high speedrelay, operates.

A'Relay TA at its contact-tal substantiates the i.

removal of vshort circuit from 'its own winding, inV

operations for the other groups but these are of no interest for thepresent purpose.

The allotter eventually reaches a position in which wiper I is inconnection with one of the contacts to which wire I9 is connected andwiper I3 is in connection with a contact, in a corresponding part oflevel I3, to which a wire la of an idle indirectly connected line-finderis connected, the idle condition being indicated by negative on the saidwire Za. In this position the following circuit is closed: earth,through rectifier RE, by way of contacts md5, 7a5, adlI, ab5, d5, ua2,wire I9, a contact in level I5, wiper I5, contact ads, windings LAG) andL.A(II) of relay LA,

contact ac5, wiper I3, a Contactin level i3 of the.

allotter, wire Za of the idle indirectly connected line-lnder, (Fig.'7), contact M2, resistance RF, wire tf (Fig. 9), contact gcI (Fig. 9),to negative. Relay LA (Fig. 5) operates.

It may here be convenientlyshown that, had Y the allotter encountered anidle directly connected line-lnder, either as it passed through thepositions between that at which it'stood when rst taken into use andthat of the i'lrst indirectly connected line finder or, thereafter, asit passed through the positions between its normal position and that ofthe first indirectly connected line-iinder, the circuit for relay LAwould have been from earth, through rectifier RE, by way of contacts ma,q'a5, acl, ab5,.d6, wire I, a contact to negative.

in level I5 and wiper I5 of the allotter, contact ac5, Wiper I3 and acontact in level I3 of the allotter, wire la of such idle directlyconnected line-finder (Fig. 7) there being no difference betweendirectly and indirectly connected line-linders so far as theirconstruction and circuits are concerned, wire pf (Fig. key HK, contactm05, wire pb, contacts pf I and ral, and resistance RO Relay LA wouldhave operated. It will be self-evident that if wiper I5 had been in aposition beyond those to which wires IU and I9 are connected, that is ina position corresponding to wires 9 and i8, the wipers would have topass through normal to reach a position in which it could serve adirectly or indirectly connected line-finder suitable for the purpose inhand. Relay UA would thus become operated but, of course, a directlyconnected line-nder would have been Y allotted before an indirectlyconnected one were reached.

Relay LA (Fig. 5) at its contact-Zal short circuits its own windingLA(I), applies earth through its own winding LA(II) which is of lowresistance, to wire Za in order to render the linei-lnder unavailable toother allotters and to hold relay LA operated, removes the short circuitfrom the windings of relays MA and NA, and opens the circuit of latchmagnet MUA. Although there is still a circuit by way of relays MA and`NA for magnet MUA, the magnet will release. Relays MA and NA operate.

Magnet MUA releasing arrests the motion of the allotter.

Relays MA and NA, which act as one relay, at their contactamal opens afurther point in the circuit of the latch magnet against the release ofcontact Zal, ma2 (Fig. 6) performs an operation of no present interest,since in the supposed case, relay AB is not operated, ma3 short circuitswinding LA(II) of relay LA and applies full earth'to wire la' tomaintain the indirectly connected linefinder `of Fig.-7 unavailable toother allotters, mail close alternative circuits for'relays AC andy AD',and relay JA, ma5 open the marking circuit, nal (Fig. 5) `prepare alcircuit for relay PA, naz close a circuit (earth, via contacts paLfqaI,m12, a02, wiper 3 of the allotter and a contact in its level 3, wiremaf, latch magnet MUF of the line-f nder, negativehfor magnet MUF, mz3prepare a'circuit to wire hf (Fig. 7), na4 close a circuit via wire deffor winding DF(I) of relayDF, na5, prepare a circuit to wire rf, andyJaSv close a circut from negative, via contacts 11.0.6, cd2, wiper I Iof the allotter and a contact in level II, wire sf (Figs. '7 and 8),relays SO and ST (Fig. 10) to earth. Latch magnet MUF energizes. RelaysDF and SO operate. (Relay ST does not k operate.) 'W

Latch magnet MUF controls the motor of the line-finder in thesame manneras that in which magnet MUA controlled that of theallotter. Relay DFeffects wiper switching, and relay SO controls the secondary allotter.The line finder and the secondary allotter operate simultaneously Itisinconvenient to consider theseoperations' concurrently; considerationlof VLthe, secondary, al- 1' lotter will be deferred. Y .7 Relay DF atits contactaafl prepares a holding circuit for-its winding DF(I), djZprepares a holding circuit for its winding DF(II) the purpose of whichwill be explained later, andldf3 to dfl effects the necessary changeover ofthe wipers. (Relay DF would not have been operated ifA the;caller had been in any of the sub-groupd of one hundred lines thestarting wires o f which arel IWX, ZWX, 3WX or IIWX for then one of the.

relays A, C, E or G (Fig. 3) would have been operated and, as shown in apreceding digression, would, at contacts a5, c5, e5 or g5 have broughtabout the operation of relay AB which relay, at its contacts ab2 wouldhave opened the circuit for relay DF.) 1

Latch magnet MUF unlatches, and starts, the

motor of the indirectly connected line-llrlderQ- Ll'5 which is assumedto be resting in a position other than that of the line of the caller.The line nder wipers are rotated and, when they en-V counter thecontacts of the caller, a circuit is completed from earth, throughrectifier RE (Fig. 5), winding PA(I) and PA(II) of relay PA, con-.Itacts nal and acI, wiper I and a contact in level I of the allotter,wire pc (Fig. 7) contact dfh5,f (say) the full line wiper and level PIof the linefinder, wire ps of the calling line, contacts ZsI and 7635,resistance RS to negative. Relay PA-(Fig.

5) operates. f

Relay PA at its contactapm .short circuits winding PA(I) of relay PA,connects earth to lowVv resistance winding PA(II) vof relay PA toprotect the calling line from intrusion and to hold relay PA and opensthe circuit of latch magnet MUF whereby the line-finder is broughttorest. I

(Wire rf of directly connected line-finders is permanently connected toearthA so that, had thev line-finder which the allotter allotted beenadirectly, instead of an indirectly, connected one, relay RA (Fig. 5)would have operated when oo ntact na5 became closed. Relay RA wouldhaveat its contacts: ral prepared a circuit for relay QA,'and 111.2substantiated contact 7a3. When, underv these conditions, relay PAshould operateit would, inladdition to the operationsnoted above, removea short circuit from relay QA and; this relay would operate, at thistime, in series.

with-riatchmagnetmur. ,'rhe-resmts orareifop;

era-tionfof relay-,QA will' be described Whensits:

operation is-referred toini connection-withthe indirectly connectedlineflnderf. L

Nothing more happens in the primary allotter until the secondaryallotter has allotted 'a sec-V ondary line-finder.

"The indirectlyv connected. line-finder having beenset on the contactsof the. callingline, consideration may` now be given tothe secondaryallotter which was left with its relay SO operated.

. (Relay SVT/operates only if two primary allotters servingthe samegroup of indjrectly'connected 1 ine'4nders,fwhich,it will be recalledare, so. far as the secondaryV allotters are concerned, dividedintortwolgroups, arev calling simultaneously for thel services of asecondary allotter.)

VRelay SO (Fig. at its contacta-sot (Figli) closes a circuit for relay I(Fig.V 12,). Rela'yl operates.

Relay I at-z'ts ontacts-ilfclsesa holding circuiti for itself tWherebyfit is rendered independent offcontactLsyl, iZlQig. 11) opensitsownoriginal operating circuitso that the starting circuit` (contact soI) v shall notfbepassed onto` a second a1 lotter, z'3'(Fig.l 13), closesa marking circuit'to wire-[Utiform the secondary allotter which half ofits levels it has to serve;`and i4 (Fig. 12) clases acircuit for relayEB.` Relay@ EBoperates.

Relay EB atz'ts"contacts.ebl opens the circuit of relay SJ-fso-that thisrelayreleases and pro? tects theallotter from calls for secondary duty(it is protected from further calls'for primary duty by` contactIiZ')`Aand prepares I a holding circuit for relay EB, eb?r prepares a circuit,at present open at' contactvv s2,` for latch magnetf MUB, eb3f closes acircuitI for relay PE, eb4 closes acirouit for re-V lay UB', e175 placesa short circuit' across vWinding QB(I) of relay QB to-renderthislrelayfretarded in release, and eb preparesY a circuitifor relays FB(Fig. 1-3') and GS (Fig- 8). RelayUBL-'operates if theY allotter'is ina-positionother than' normal with results of no present interest.RelaysFB and GS'opera-te if; or as soon as, Wiper 8` of the v secondaryallotter isassociated With a contact ofthe half of level 8 to which wireVIllg'isi-multipled` and if, or as soon as; Wiper 'ly of thesecondaryallotter is associated with a contact of! the corre?v spendinghalfof level'lto'Wliich-awire-gs ofan availablesecondaryline-nder isconnected Ref lay PE'(Fig-. 13) operates:

Relay PEA at its contacta-pel closesa-circuit for Winding QB(II) ofrelay QB, and pe-Z'l (Fig. 12) substantiates contact eb'l. Relay QBopcrates.

Relay QB at its contacter-:16| vguards itselfv against the opening ofcontact rb3, qb2`prepares al short circuitlfor relay'Pll,v qb?.preparesa circuit for relay S, and qb4-closes a circuit for retardedoperatingy relay RB. l Relay RB after a delay, operates;

Relay RB-at its ,contacter-rIJIy closes a holding` circuit for itself,1'b2" preparesl a short circuit acrossitsown Winding, T631 opens theoriginal circuit for relay QBWhich relayis now held by contact qbl, rbt,preparesv a circuit'towiper 3- ofV the'secondary allotter, rbcloses acircuit for relay S, andA rbcompletesa--short' circuitl across relay-PE.Relay PE does not release immediately. Relay S operates. The reason for.this chainof operations and of the very retardedl release of` relay PEwill be understoodV later:

Relay-S at its 'contacta-46| fopens the circuitofv relay PEI and closesa holdingv circuit; for'itself, s2: closesia' circuiti from earth at`contact fbi', sup,-

allotter'nds'these funavailable.

tion" of no4 present interest.

The secondary allotter may notor. may have` itsrwipers already in:association with the contacts of a lsuitaloleand availablefsecondaryline.-

finder.V If ithas not, latch magnet MUB Willbei.

energized and the allotter vvillV rotate to lndfa suitable and availablesecondary line-finder. If 'itV has, or as soon as ithas, Vrelays FBv andGS will operate as described above.v

Relay GS at. its cofttacts'f-gslV removes one source of earth fromwiregc (Fig. 9) and'gs2 prepares a circuit for relay NS.

(When allsecondary line finders are in use, all" sources of earthareremoved from: wire gc and relay GC (Fig. 9) operates. Relay'GC at itscontact gcl' removes negativefrom Wires tf of all indirectly connectedline-nders served by the secondary lneenders ofthe group to Whichthatshown in Fig. 8A belongs. so that the primary into' operation only whennight service is Vin force.)

Relay- FB (Fig. 13)l atiits contact fblopens the circuit of latchmagnet'fMUB, remo-vestlie short circuit from relayl-l-'Bi and shortVcircuits windingFB(I) of-relaylB.l Latch magnet MUBire` Yleasessandl`arrests the motion of the allotter andY relay operates in series Withmagnet ReZay'HB at its contacta-kbl' substantiatescontactf fblinsofaras'that contact is related to relayl HB and to latch magnetMUB-hb2A prepares a circuit from earth through rectifier RC (Fig. 13),windings JB(I)*and1JB'(II) of relay JB, contact lic2,wiper |-and`thecontact in level I at which wiper If is resting, to wire am, hb3 closesa` circuit from earth, by way of contact jl, lb2,

the-latch magnet forY the cordseeker, to negative,

hb'lv opens-the'circuit of relay UB, vides a locking circuit for relayEB".

Latch magnet MUS may-or may not operate as thesecondary line-finder isnot or is already servingl the indirectly connected line-finder whichcalled for service. If it is already,or as soon` as it is, servingthatindirectly connected line-nder, the4 circuit above noted` as preparedfor relay- JB to Wire'am'is'further extended by Way of Wiper AM of thesecondary line-lnder, the appropriate contact in level AM, Wire rf (Fig:7), the appropriate contacti'n'level 9.`(Fig. 5) of the primaryallotter,.wiper 9,' contacts adl and na5, and relay RAV shunted byresistance RR, to negative. Re.- lays JB"(Fig. 13)andRA (Fig. 5)operate. (The and hbl proeffects ofthe operation of relay RA Will bedescribed later. All that need be stated .at present is thatv iteventually brings about the breaking, at

Relay NS comes- .AM of the secondary line-nder'protects the inL directlyconnected line-finder from intrusion by,

allotter to Wire pl and thence by way of Wiper P and level P of thesecondary line-finder to wire pf to hold relay BF and Winding DF(I) ofrelay DF in the indirectly connected line-finder, Z115 and Zb bridgescontacts nb and 12224 to guard relays I and EB against release Whenrelay NB becomes operated and lb'l performs an operation of no presentinterest. Y

Relay NB at lts"co1ztacts.-nbl further pre-A pares the'circuit alreadypartly prepared by con,- tact rb@ to Wiper 3 Vof the secondary allotter,hb2

vopens a point in the original operating circuit of relay LB to guardthis relay against an eventual Y releasecf contact lbLnbS and nbllperforms operations of no present interest, and nb sube stantiatescontact eb! insofar as rthat Contact is related to relay SJ. (All thisoccurs Whilst relays PE and relays which it controls are stilloperated.)

At the same time that these operations, which include a possible searchby the secondary linender for the calling indirectly connected linenderand which include either the immediate or eventual operation of relaysJB (Fig. 13) and R (Fig. 5) followed b-y theA operation of relaycLB,have been taking place, latch magnet MUC may or may not have operated asthe cord seeker may not cr may be already serving an idle cord-circuit.If it is already, or as soon as it is, serving an idle cord-circuit, thecircuit above noted as prepared for relay KB to wire ps becomes furtherextended by Way of wiper PC of the cord-seeker (Fig. 8), Wire pc (Fig.15.), contact l ofkey HK, contacts mcE, pil, and mi and'resistance RO,to negative. Relay KB (Fig. 13) operates.

Relay KB at its contact kbl short circuits Winding KB(I) of relay KB,provides a holding circuit by way of winding KB(II) for relay KB, and byraising the potential of the contact in level PC of the cord-seekerprotects the selected cord from intrusion by other cord-seekers, andopens the circuit of latch magnet MUC and removes a short circuit fromrelayY MB. The cord-seeker is thus brought to rest and MB becomesoperated in series with the latch magnet.

Relay MB at its contactsmw substantiates contact Ich! insofar as thatcontact is related to relay MB and to latch magnet MUC, and mb! places abridge across contact lb2 for the eventual release of relay LB.

' By this time relay RA in the primary alljotter should have broughtabout the opening of con.- tact na and the consequential release ofitself and of relay JB in the secondary allotter.

Relay JB at its contact ybl provides a short circuit for relay LB. RelayLB becomes released.

Relay LB at itsL contacta-elm and lb2 performs restoratory functions,lb3 opens the circuit of relay NB which, however, is of retardedrelease', and closes a circuit by Way of Wiper and level 3 of thesecondary allotter for relay HS (Fig. 8), lb4 removes earth fromWire'pl, lb5 and lbl (Fig. l2)

short circuits relay RB. Relay HS (Fig. 8) becomes operated and relays Iand EB become released. Relay RB becomes released after a delay. RelayHS at its contactaml closes a holding circuit for itself to Wire ps andopens the circuit of relay KB, Rs2 substantiates contact gsi insofar asthat contact is related to relay GC, (Fig. 9) and replaces the earthremoved from Wire pl by contact Z194; hs3, hs4 and hs5 extends Wires-l-f, -f, and mf, to wires +S, -s, and ms; hsl performs an operation ofno present interest; and hs prepares a circuit for relay CH. Relay KBreleases. The calling subscribers line isnow eX- tended through anindirectly connected and a secondary line-finder (Figs. 7. and 8) to acord circuit (Fig. l5).`

Returning now to the secondary allotter, relay I lat its contactsperforms restoratory operations,

relay EB at its contacts performs restoratory operations including thepreparation of the circuit for relay SJ, (Fig. ll) the opening of thecircuit for relays FB,Q(Fig. 13) and GS (Fig. 8) and of the'circuit forrelays HB and S. Relay KB short circuits relay MB. Relay'I-IB performsrestoratory operations. have become released, performs restoratoryoperations, including therfurther preparationof the circuit foi-,relaySJ.

Relay PE which Will have become released by now, performs restoratoryoperations including the closure of the circuit for relay SJ, andtheopening of the circuit for relay QB. Relay QB performed restoratoryoperations. Relay RCB` also performed restoratory operations.Thesecondary allotter is thus restored toits normal condition.

(It may here be mentioned that if for some reason o-rother` thesecondary line finder had been. unable to nd the calling indirectlyconnected line-finder, relay JB Would not have operated and thereforerelay LB would have remained-unoperated. Relay PE would, as: wasdescribed above, have becolme short circuited by contacts qb? and rb@when those relays became operated and would consequently, after a delay,have become released. Relay PE would at its Contact pel have opened thecircuit of relay QB which, after a delay due to its Winding. QB(I) beingshort circuited, Would have become released. RelayQB at its contactcgb-3 would have closed a circuit for relay TB and at qbl shortcircuited relay RB. v RelayRB, after a delay, Would have become releasedand would have at its contacts ThV opened a possiblecircuit for VrelayHS and TD5 closed a circuit for relay NB. Relay NB would have becomeoperated and would have at its contacts no3 and nb opened the circuitsof relays I and EB (for which no guards would have been closed by relayLB), and 11125 kept open the circuit of relay SJ. Relays I and EB wouldhave released. Relay I would have at its contact i2 (Fig. 1l) reclosedthe start circuit Which opensfthe circuits of relays I and EB, and ZblRelay NB, which, by now, Will'r would be consequently passed on by thecontacts.`

sy'l and ski to allotter numb-er 2. Relay EB would have brought aboutthe release of the allotter Which failed.)

The description ofthe primary allotter was left at` the point that itsrelay PA had operated and had, inter alia opened the circuit of .latchmag.- net MUF. It was also mentioned in the description of the'secondary allotter, that relay RA in the primary allotter becameoperated. "The, ef. fects produced by this operation Will nowbeconsidered.A 7 H RelayiRAlat its contacta-#ral 'closes acircuitfor relayQA inlserieswithl latchmagnet MUF,.

and mZFSubstantiates'contact 7a3. Relay QA becomesoperated but. notlatch magnet MUF.

Relay @Aat its contacts-aal. closes-a holding circuit;via resistanceA RQfor relay QA, qa2 opens the circuiti of winding KAG) of relayKA andVclosesacircuit for relay HF (Fig. '7), qa3 sub-` stantiatesf contact7a3, qad opens .the circuit of relays MA and NA, qa5 closes acircuitforwinding AEG) of relay AE. Relay KA. becomes released, relay HFbecomes operated, relay MA and NA. become released, and relay AE.becomes operated.

Relay KA: at its contacta-km to ka3 and lca5l to kat performsrestoratoryoperations and lca4 opens the circuit of relays VTA and UA.. Relays TAand UA become released.

Relay HF aet'zts `contacts-itil `closes a holding circuit for. itself towire pf to which wire earth has by now beenconnected either by relayLB`in thesecondary allotter or by relay. HS in the secconnected to wirepc short circuits winding PAGI) o-f relay PA. Relay PA becomes-released.

Relays MA and NA at their contacts-. -mal preparea circuit for latch.magnet' MUA as will appear, ma2" to mail' perform. restoratoryoperations, mali reprepare the marking circuit as willappear, nalperform a restoratory operation,v mi2 open a pointin the circuit oflatch magnet` MUF to guard that magnet against an eventual release ofrelay QA, mz3 and m14 perform restoratory operations, m15 open thecircuit of relay RA, and nai perform a restoratory opera-A tion. RelayRA becomes released.

ReZayAE at its contacta-aeI-'removes a short Circuit from winding AEGI)of relay AE, aeZ7^ opens the circuit of winding JAG) of relay JA, ac3substantiates contact gia3; aed places a bridge across Contact 1a5.tomaintain .a marking potential on Wire I D, ae preparesa circuit forlatch magnet MUA, aeB performs an o-peration of noY interest in the caseunder consideration, aeI closes a holding circuit for relay D (Fig. 3)which circuit is independentof'the condition of start wire Zyz, and @e8prepares a circuit to the initial contactsof level I3.

Relay TAv performs a restoratory operation. Relay UA performsrestoratory operations ncluding particularly, theA disconnection ofmark-V ing wire I9 from marking wire I0.

Relay PA at its contact pal short circuitsv relay QA. Relay QA becomesreleased.

Relay RA performs restoratory operations..

Relay QA at its contacts-aal to qa3 performs restoratory operations,qad'closes a circuit from earth at contact laI, by way of Ycontact mal,

ae5', qa4, winding AEGI) Yof relay AE' andV of latch magnet MUA, tonegative,V and' qa5 opens thercircuit of winding AEG) of relay AE. whichrelay is'however held over its winding AEGI). Latch magnet MUA 'becomes'energized.

Relay JA at its contacta-#MI to 1'a3 and y'a5 performs restoratoryoperations, and 7a4 completes the connection of negative to the initialcontact inlevel I3.

Latch..magnet MUA unlatches, and completes the motor circuit of,. theallotter whereby the allotter is driven to its'initial position. When745 the initial position is reached, a circuit is completediromearth.atvinitial Contact in level ISLV by way of wiper I5, contact acl3, windingsLAG) and LAGI) of relay LA', contact ac5, wiperA I3, Y

initialcontact in level I3, contacts gaIIand lca, resistance RK, tonegative. 'Relay LA becomes operated. y

Relay'LA at its contact Zal opens the circuit of` latch magnet MUA andof 'winding AEGI) of'` relay AE'v and short-circuitsl winding LAG) ofIrelay LA. LatchvmagnetMUA and relay AE moves negative from the initialcontact in level-v I3 and opens the circuit of winding LAGI) of relayLA. Relay SJ operates and relays D andV LA released. K

Relay SJ reconnects the start WiresA wr and ye to relaysv A to H.

Relay D at its contacts-dl to d4 performs restoratory operations, d5opens the circuit of winding4 AAG) of relay AA, and d6 performs a.restoratory operation.

Relay LA performs restoratory operations.

ReZayA'A` at its coatacts..-aa| performs a restoratory operation, aa?opens the circuits of re.- lays AC and AD, and AA3 performs arestoratory operation.V Relays AC and AD become released...

Relays AC andAD perform restoratory opera.- tions (mainly wiperswitching). i

Gf the allotter had allottedany directly connectedgline-nder of a group,yexcept the last directly connected line-finder of that group insteadof, as has been supposed, an indirectly connected line-nder, it would,in travellingtowards its initialposition, have passed the contacts ofintervening directly connected line-finders of the group from which ithad just previously allotted one. If one. of these intervening directlyconnected linefinders had been idle, that is had had negativepotential'on its Wire la, the following circuit would Y rectifierRE,.con`tacts ma5, ae4, abi, d6',.,wire I Il,

a contact in level' I5 to which wire II) is multi'- pled, wiper I5',contact 'ad3`, windings LAG) andr LAGI) of relay LA, contact co5, wiperI3'in the position in which it encountered the contact of the idledirectly connected line-finder, to negative Aon Wire la of thatline-nder. Relay LA wouldhave operated with resultsas above. The resultwould have been thatthe allotter, instead of. going Vto itsinitial'.position, would-have preallottedv an. idle. directly connected line nderready for. usejin anticipation that the next call would.v originatefrormthe same group.)

Gt is here convenient toV explain. that, if the allotter has been unableto nd a suitable linefinder, either directly connected or indirectlyconnected, in. an idle condition, it would continue to rotate untileither theA contacts-designatedz, which are timed contacts, opened orthe calling subscriber hung up. In.the former case, one of thejcontactse wouldhave opened the circuit of. relay KA4 Wherebythe. circuit of thelatch magnet wouldhave been. openedand other restoratory operationswouldhave been. performed.

InA the. latter case, relay D would. have become.

releasedwith results.- leading up by way of the.v

release of relay AA to the release of relay JA.

Relay JA at its contact 7a4 would have prepared a circuit for relay LAin the initial position of the allotter as follows: earth from initialcontact in level I5, wiper I5, contact ad3, windings LAG) and LAGI) ofrelay LA, contact ac5, wiper I3 and initial contact in level I3,contacts :aA and ka, winding KAGI) to negative. The current in windingKAGI.) of relay KA would be in opposition to that in Winding KAG) andthereby relay KA would have become released.)

The primary allotter is thus released as is also the secondary allotter.It will be recalled that a primary allotter requires from a linender, inorder that it may recognize the linender as being available for service,negative on wire la. A secondary allotter requires from a secondaryline-finder negative on wire g's.

Subscribers lines are of two sorts, that is they have differentfacilities, and they will be termed A and C subscribers respectively.The meters MS of A subscribers are connected to negative and requiresearth impulses from the cord circuit for their operation: those of Csubscribers are connected to earth and requires negative impulses fortheir operation. It will be assumed that the caller is an A subscriber.

As soon as a calling subscribers line has been extended to acord-circuit (Fig. 15) either by a directly connected line finder by theclosure of contacts hf3, hill Iand. hf@ or by an indirectly connectedand secondary line-finder and cordseeker by the closure of contacts hf3,hfd and hf and hs, hsll and hs5, circuits will be completed for windingLCG) and LCGI) of relay-LC and for winding BTG) of relay BT, the lattercircuit being in series with meter MS. Relays LC and BT become operated.Moreover, the caller receives calling tone. The subscribers meter doesnot become operated in series with relay BT. Relay BT at itscontacta-bil prepares a circuit for winding BTGI) of relay BT, blt2preparesja circuit for calling lamp AC and opens a possible circuit forcalling lamp CC, and bt3 prepares a point in the meter circuit to wiremc to meter a call to an A subscriber (earth connection).

Gf the calling line were a C line, no circuit would have existed forrelay BT, lamp AC would not have become switched in and lamp CC wouldnot have become switched out. The metering circuit would have been leftfor the metering .of a call to a. C subscriber (negative connection)Relay LC at its contactalol closes a circuit for relay BC, Zc2 opens apoint in the circuit of lamp CC' which is also the supervisory lamp forthe calling side of the connection and lc3 and lc4 opens circuits whichhave no present interest. Relay BC becomes operated.

Relay BC at its contacts-bcl connects earth to wire pc (or pf) to renderthe cord circuit unavailable to other calling lines, be2 performs apreparatory operation, bcS opens a point in the meter circuit forleither an A or a C subscriber, bc closes a circuit for lamp AC and forrelay PC (Fig. 16), bc5 closes a circuit for windings MCG) and MC (III)of relay MC and for winding NCG) of relay NC, and bc removes one sourceof earth from relay CG, (Fig. 9). Lamp AC glows and relay PC becomesoperated. Relays MC and NC do not become operated. y

(This operation of removing earth from relay CG is protective operation.If earth is removed entirely from relay CG, that relay will operate andrender further secondary line nders, which serve the cords concerned,unavailable.)

Relay PC at its contacts 'pcI closes a circuit for relay PF. Relay PFbecomes operated.

Relay PF at its contacta-MI substantiates Contact bel, pf2 and pf?,disconnects calling tone from the cord-circuit and connects thecord-cir-Y cuit to the operators service circuit CP, pf4 disconnectsearth from relay BC but this relay still holds to earth at release keyRK, 201 opens the circuit of relay PD, and pfIi closes a circuit whichwill be described later and which'causes three so-called pips of tone tobe connected to the calling line via the cord, and causes the last ofthese pips to be heard by the operator. The three pips are to notify thecaller that he may give in the number he requires and the one pip is tonotify the operator that a number is about to be given in. 1

It should be explained that the cord circuits on an operators positionare divided into two divisions which may be termed PC-cords and PD-cordsbecause, when a call arrives on a PC-Y cord, relay PC operates and, whena call arrives on a PD'-cord, relay PD operates;Y When a call arrives ona`PC-.cord, contact pfI connects earth toall the lPC-cords so Vthat noother PC-,cord can-be taken into use, that is the rPC-cordsare marked asunavailable tothe cord-seekers. PD- cords are not yetrenderedunavailable but relay PD cannot become. operated nor can thecalling lamp of a PD-cord be lit. Moreover, the g, earth, connected'bythe relay BC offa calling PD-cord tothe wire'qoc of such PD-cord, is fedby way of'wire pd to other -PD-cords. Itv thus arises that the operatorcan receive one visible call on a cord of one sort and'one invisiblecall 4 on a cord of the other sort. f

When the operator has ascertainedthe callers requirements and has takenup the plug of the cord to which the caller is connected, which cord isidentified by the glowing lamp AC, she will insert this plug into thejack, such as JM, of the wanted subscribers line. That line may be free,in which case there will be negative pov tential connected to the-private wire 10m, or itj may be already engaged, inwhich case therewill be positive potential connected to vthat wire. These conditions maybe verified by reference to Fig. l, the line there shown being, for thepurpose, regarded as that of the wanted subscriber.

When the operator lifts the plug from its seat on the plug-shelf,contact ps becomes closed and completes a circuit for winding BTGI) ofvrelay BT (already operated) and prepares other holding circuits. Y,

Suppose the wanted line to be free, then when the plug is inserted intojack JM, a circuit will become completed from earth, via contact bc,winding NCG) and MCG). of relays NC and MC, contact m09, sleeve of theplug and of jack JM, wire pm (Fig. l) regarded as the' equipment of thewanted line, contacts ls4 and lcs5,

resistance RS to negative. Windings LSGI)v of relay LS and KS GI) ofrelayvKS in series are in parallel with contacts 1655 and resistance RS.Relays NC, MC, LS and KS operate.

Relays LS and KS at their contacta-152 and,

Rs2 disconnect earth from wire -l-s ofthe wanted line, ls?, and ksIdisconnect winding LSG) and KSG) from wire -s, lcs3 guard winding LSGI)and KSGI), 74:84 open the circuit to the start wire, and ks disconnectnegative `via resistance RS from wire pm.

Relay MC at'zts contactamel closes a circuit for Vwinding MCOI) forholding relay MC operated, mc2 and m03 disconnects the cord-circuit fromthe operators service circuit, m04 closes a circuit for calledsupervisory lamp CS, m disconnects wire pci-rom the common positionequipment so that any earth connected to wire pc is not fed to wires pcof other PC-cords, met disconnects winding BT`(I) from wire mc, melclosesra circuit for retarded release relay JC, mcs closes a holdingcircuit for relay BC, m09 opens the circuit for windings NC(I) and MC(I)of relays NC and MC, and moll) substantiates contact bcG. Lamp CS glowsand relay JC becomes operated.

Relay NC' at its contacta-ncl closes a circuit for winding NC(II) ofrelay NC to hold this relay, nc2 and no3 connects the plug to contactsfel and fc3, no4 closes a sneak circuit for ringing tone, m5 connectsearth to the plug and thus to wire pm to mark the wanted line busy.

Relay .JC at its contacta- -lcl connects earth to wire pc in addition tothat already connected by contact bel, je! and fc3 connects a source ofringing current, over leads rc and winding FC(I) of relay FC, to thewanted line, ic4-closes a further point in the meter circuit, fc5performs an operation of no present interest, and ics disconnects thecalling lampI ACfand relay PC. The calling lamp darkens and relay PCbecomes released, and the wanted subscribers bell is rung.

Relay PC at its contact pel opens the circuit of relay PF. Relay PFbecomes released.

Relay PF at its contacts perform'restoratory operations which includethe preparation of the circuit of relay PD so that an invisible call ona PD-cOrd, if there be one, may become visible. Further operationsdepend upon the behaviour of the calling or called subscribers. Normallythe called subscriber replies.

When the called subscriber replies, a circuit is completed, through theloop of his telephone instrument; for relay FC. Relay FC operates.

Relay FC at its contacts-fel closes a circuit for winding FC(II) ofrelay FC, fc2 and fc3 disconnects ringing leads rc and connects the plug(and thus the called subscriber) through to the feeding bridgeconsisting of relay DC and coil RC and also to the calling line, fc4closes a point in the meter circuit alternative to that closed bycontact ncl, fc5 prepares an alternative circuit for winding NC(II) ofrelay NC which it renders independent of contact be2, and fcG preparesan alternative circuit for winding LC(I) of relay LC. Relay DC becomesoperated.

Relay DC at its contacta-del closes the alternative circuit for windingNC(II) of relay NC, a02 opens the circuit of the called supervisory lampCS, and ac3 and dell prepares circuits which have no present interest.

When the conversation is ended,V either sub- A scriber can, by hangingup his telephone, render his own line available, for use either for theinitiation or receipt of calls. For rendering the line Yfindersavailable it is necessary that both subscribers hang up theirtelephones.

Suppose that the called subscriber hangs up his telephone rst. Relay DCbecomes released and at its contact del opens the circuit of windingNC(II) of relay NC and dc2 closes the circuit for supervisory lampCS.Lamp CS glows and relay NC after a delay, becomes released.

Relay NC at its contacts performs restoratory operations, only two ofwhich needn be considered namely that at contact n'c5 it removes earthfrom wire pm of `jack JM and thus releases the called subscribers relaysLS and KS, and at contact ncl appears to effect a change in the metercircuit which, however, is guarded rby" contact fc4. By the release ofrelays LS and KS, the called subscriber is enabled to receive and toinitiate further calls.

W'hen the calling subscriber hangs up his telephone relay LC becomesreleased.

Relay LC at its contacts lcl opens the circuit of relay BC, and lc2closes the circuit of supervisory lamp CC. Lamp CC glows and relay BC',after a delay, becomes released. Y

Relay BC at its contacta-hcl removes vone source of earth from wire pc,be2 opens the circuit of relay JC, bc3 closes the meter circuit for an Asubscriber by connecting earth'via contacts bt3, 7a4, bc3,fc4, to wiremc, Z205 opens the circuit of windings MC(I) and MC(III) of relayMC andof winding NC(I) of relay NC, and bell Vand 1906 performs restoratoryoperations. The calling subscribers meter becomes operated Yand relayJC, after a delay, becomes released.

Relay JC at itsrcontactsr-ycl removes earth from wire pc (or pf) and sofrom relay HS (Fig. 8), y'clV opens the meter circuit, and at othercontacts performs restoratory operations. The calling subscribers meterand relay HS become released but, in the absence of negative on wire pc(or p-f) the cord does not yet become available.

Y Relay HS at its contacts-hs! reconnects wire ps (extension of wire pc)to wire kb', hs2 disconnects earth from wire pf and thus from relays HFand DF, and from wire 11|, and reconnects earth to wire ac, hsreconnects negative to wire as to render the secondary line nderavailable and at other contacts performs restoratory operations.

Relay HF at its contacta-M2 reconnects negative to wire la to render theprimary line finder available, M5 removes earth :from wire ps and thusfrom relays LS and KS of the calling subscribers line, and at othercontacts performs restoratory operations. Relays LS and KS of thecalling subscriber become released and the calling subscriber is thusenabled to initiate and receive further calls.

It will be noticed that everything is now made available for further useexcept the cord circuit, but that the two supervisory lamps CS and CCare glowing. The operator, observing the two lamps, withdraws the plugfrom jack JM and restores it to its seat. Hereby contacts ps (Fig. 15)open the circuits of windings BT(II), FC(II), and MC(II) of relays BT,FC, and MC and these relays become released.

Relays BT and FC at their contacts perform restoratory operations, andrelay MC at its contacts: 'mail opens the circuits of the supervisorylamps, m05 rreconnects negative to wire pc (or pf) to render the cordavailable for further use, and at its other contacts performsrestoratory operation.

If the called subscriber had not replied, relays DC and FC would nothave become operated. With these conditions, as soon as the callingsubscriber hung up his telephone, his line would have become released inan exactly similar manner to that described above except that the metercircuit would have extended from earth, via contact btS, icd, Z703, ncl,and fc4 to wire mc.

If the wanted subscribers line had been already engaged there would havebeen earth on wire pm of jack :im and consequently there would have beenno circuit for windings MC(I) and NC (I) of relays MC and NC. On theother hand there would have been a circuit for winding MC(III) of relayMC. Relay MC would have performed its normal operations. Busy tone'would have been connected to the calling line by way of contact no6 (atrest) and metering would have been prevented by contact nel.

If the calling subscriber had asked for an un available number, that isfor the number of a non-existent subscriber, the operator would haveinserted the plug into jack NU (Fig. 14) and matters would haveproceeded as for a correct call. The called supervisory lamp CS wouldhave been caused to ash.

It will have been observed that a calling subscriber is entirelyanonymous. It may have been observed also, that when restored toservice, the primary and secondary line-nders and cordseekers were notdisturbed from the position they had occupied but were merely renderedavailable for fresh service. If they are taken into service again it isprobable that their positions will be disturbed and the two line-finderswhich have been in association may not be associated for a succeedingcall; thus all chance of identifying the previous caller will be lost.It may be, moreover, that the anonymity of the calling subscriber ismaintained throughout the connection and yet the called subscriber maywish to destroy the anonymity of the caller. To this end it is arrangedthat if the called subscriber, who wishes to destroy the anonymity of acaller, does not hang up his telephone, the line-finders andcord-seekers are not rendered available for service but remainassociated with the circuit with which they were last used. Thus, thecord-seeker (if one was used) will remain with its wipers in associationwith the contacts of the cord-circuit, the secondary line-finder (if onewas used) will remain with its wipers in association with the contactsof the indirectly connected line-finder, and the primary line-finder(indirectly or directly connected as the case may have been) will remainwith its wipers associated with the contacts of the calling subscriberwho was responsible for their use and whose identity it is desired todiscover, and moreover, these pieces of apparatus will be maintained inan unavailable state (no negative on wires ys and la) though the callerwill be released and be able to initiate and receive calls.

The are as follows: As

clearing operations under these conditions the called subscriber has nothung up his telephone, relay DC will not be released and lamp CS willnot glo-w. Relay DC will maintain closed its contacts ac3 and dell.

When the calling subscriber hangs up his telephone, relay LC will becomereleased.

Relay LC at its contacts-lol opens the circuit of relay BC, [c2 clo-sesthe circuit of supervisory lamp CC, Zc3 closes a circuit for relay HAcommon to the operators position, and loll closes a circuit to wire ch(Fig. 8) and thence, via level and wiper CHC, contacts 'n.86 and 1188 torelay CH. The calling supervisory lamp glows and relays HA and CH becomeoperated and, after a delay, relay BC becomes released.

Relay HA at its contacte-hal closes a circuit for a distinctive signal,such as a coloured lamp CL, at the operators position, and ha2 may closea general alarm circuit. Y

Relay CH (Fig. 8) at its contacta-chl closes a holding circuit foritself, ch2 closes a holding crcuit for relay NS should such have beenoperated,' ch3 opens a point in the circuit of relay GS, so that,'inspite vof the eventual release of relay HS, negative will be withheldfrom wire ys and the secondary line-finder will be withheld fromservice, chil closes a circuit for lamp CHL, and chE: connects earth towire cf (Fig. 7) and thus to wire la and winding DF(II) of relay DF..Relay DF is thus maintained operated in spite of the eventual releaseof relay HF' and the earthen wire vla maintains the indirectly connectedline finder in'an unavailable state.

Relay BC (Fig. 15) at its contacts.-bcl removes one source of earth fromwire pc, be2 opens the circuit of relay JC, and at other contactsperforms other operations as before. Relay JC becomes released.-

Relay J Cat its contact :icl removes earth from wire pc and thus fromrelay HS, and at its other contacts performs other operations as before.Relay HS becomes released.

Relay `HS at its contact 71,82 removes earth from wire pf and thus fromrelay HF, and at its other contacts performs other I operations. asbefore. Relay HF becomes released.

Relay HF at its contact bf2 reconnects negative to wire la (but thisnegative is short circuited by the earth from wire cf), hf5 removesearth from wire ps and thus from relays LS and KS of the callingsubscribers line. Relays-LS and KS become released and thev callingsubscriber isV thus enabled to initiate or receive further calls. Y

(If an indirectlyconnected line-finder had not been employed, but,instead, a directly-connected one had been employed, Vthe earth placedupon wire ch would appear on wire cf with results similar to thosedescribed.)

The operator seeing lamp be able to ascertain which CL glow will easilycord has connected to it a called subscriber, who wishes to establish..

the identity of the subscriber who called him, by observing which cordhas its calling supervisory lamp CC glowing and its called supervisoryylamp CS darkened. The operator is able to have the connection traced byan observation of the positions of the several switches, assisted by anobservation of lamp CHL.

If, at the stage at which the calling subscriber has establishedcommunication with her, the operator wishes to hold up the connection,do so -by the operation of key HK, which, by maintaining earth on wirepc, holds relay HS (or HF) and thus relays LS and KS of the call-` ingsubscriber. Under these conditions not only are the line-finders andcord rendered unavailable but also the callingY subscribers line is notreleased.

There now remains to describe the manner inV which three so called pipsof tone are counted, the manner in which they are made audible to thecalling subscriberand the manner in which the last pip is made audibleto the operator.

It may berecalled that the sequence of operations which led to thiseiect was, relay LC brought about the operation of relay BC, relay:

BC brought about the operation of relay PC, relay PC brought about theoperation of relay PF, and relay PF closed its contacts pf. Relay UOtherefore became operated. v

Relay UO at its contactaaol closes a circuitfor relay VO, and a02prepares a first'oircuit for relay ZO. Relay VO becomes operated.

Relay VO at its contactavol closes a circuit for relay WO, and 1102opens a point in a second circuit of relay ZO. Relay WO becomesoperated..

she may erators receiver circuit. Verated.

.Relay .WO at its contactawol closes a circuit 4for relay XO, and w02prepares a point inthe above named second circuit of relay ZO. Relay XObecomes operated.

Relay XO at its contacta-aol closes a circuit for relay YO, :no2 opens apoint in a third circuit of relay ZO, and :co3 opens a point in the op-Relay YO becomes op- Relay YO at its contacta-ym completes the firstcircuit for relay ZO, y02 opens the circuit `o1 relay UO, yo3 Yand y04connects the tone circuit 2t to the cord circuit by way of condensers Iand 2. Relay ZO becomes operated and krelay UO becomes released after ashort delay.

Relay ZO at its contacta-20|! closes a holding circuit via contact a02,202 opens a further point the already opened holding circuit, 202prepares a point in the circuit of relay UO, and 203 `opens the tonecircuit. Thus has been transmitted to the calling subscriber one pip oftone.

Relay VO at its contacta-vol opens the cir-V Vcuit of relay WO, and 1102closes the second circuit of relay ZO. Relay ZO becomes operated andrelay WO, after a delay, becomes released.

Relay ZO at its contacts-2ol and 202 performsoperations of no presentinterest,vand 203 completes the tone circuit 2t.

Relay WO at its contacter-wol opens the cir- Y cuit of relay XO, and wo2opens the second circuit of relay ZO. Relay ZO becomes released andrelay XO becomes released after a delay.

Relay ZO at its contact 203 opens the tone circuit. Thus a second pip oftone hasbeen transmitted to the calling subscriber.

Relay XO at its contactawol opens the circuit of relay YO, :co2 closesthe third circuit (via contact yol) of relay ZO, andV x03 closes thepoint in the operators telephone circuit. Relay ZO becomes operated andrelay YO after a delay becomes released.

Relay ZO at its contacta-20| closes a holding circuit (via contact x02),202 opens a point in the circuit of relay UO, and 203 completes the tonecircuit 2t.

Relay YO at its contacts yol opens the point in the third circuit ofrelay ZO (but this relay has a holding circuit) yo2 closes a point inthecircuit of relay UO (but this circuit is open at contact 202), and yo3and yo. disconnects the tone circuit from the cord circuit. Thus therehas been transmitted to the calling subscriber a third and final pip oftone. This i'lnal pip" was also transmitted, via contact x03 to theoperator.

'The automatic cyclic operation of relays UO to ZO is now arrested byrelay ZO which can be released only by the opening of contact pf or ofkey RP.

If key RP be opened and then again closes, it can be seen that thevcycle of operations of relays UO to ZO will be repeated. 'I'hisindicates to the subscriber thathe -is required by the operator torepeat the number of the line to which he wishes his own line to beextended. (It may `be observed Vthat the operator has no microphone.)

In Fig. 8 there is shown `a relay NS. During certain slack periods, suchas at night, the circuit of this relay is prepared, as by the closure ofa key. When, under these conditions relay GS becomes operated it, at itscontact gs2, completes the circuit of relay NS. Relay NS becomesoperated.

Relay NS at its contacta-asl closes a holding circuit for itself by wayof contact hs'l, m2 to us5 effects wiper switching for the cord-seekerwhereby the vlatter is caused to select a connecting circuit, such asthat shown in Fig. 17, on a night or concentration position.

When the calling line becomes connected to the connecting circuit (Fig.17) a circuit is completed over wiper MN (instead o1 wiper MC), wire ma,Contact co3 to winding BN (I) of relay BN and the subscribers loop isextended over Wipers -I-N and -N to relay LN. Relays BN and LN becomeoperated.

Relay BN at its contacta-bal prepares a holding circuit for winding BN(II) of relay BN, Ylm2 switches out lamp CN (the calling lamp for a Csubscriber) and switches in lamp AN, and bn3 prepares the meter circuit.

Relay LN at its contact Zal closes a relay BB. Relay BB becomesoperated. n

Relay BB at its contacta-bbl connects earth to Wire 1m to render thecircuit unavailable to other cord-seekers and to hold relay HS, hb2vcloses the circuit for lamp AN, bb@ opens a pointv in the meter circuit,and bbll prepares a circuit for relay JR. Lamp AN glows.

The operator seeing lamp AN glowing will, by inserting a plug in jackJN, ascertain the requirements of the calling subscriber and will thenextend the connection accordingly, all in accordance with establishedmethods. Y Y

When a plug is inserted into jack JN a circuit is completed for relayCO. Relay CO becomes operated. A

Relay CO at its contacta-col opens the circuit of lamp AN and closes thecircuit for winding BN(II) of relay BN, co2 removes negative from wire1m, and co3 disconnects winding BN (I) of relay BN and prepares afurther point in the meter circuit.

When the called subscriber replies, circuit changes take place in thecord-circuit (not shown) used by the operator which result in earthbeing connected to the sleeve of jack JN. Relay JR becomes operated. y

Relay JR at its contacta-irl connects another source of earth to wirepn, :112 closes a further point in the meter circuit, which is now openonly at contact bb3, and 1`r3 connects an alternative source Vof earthto relay CO in order that the release of that relay may be delayedsomewhat after the withdrawal of the plug.

When the calling subscriber Vhangs up, relays LN, BB and JR, in thatorder, become released. Relays BB and JR remove earth from wire PNwhereby, in the manner described in connection with Fig. 15, the callingsubscribers line is freed, and, in the interval between the release ofthe two relays contacts bbS and :ir2 effect metering.

circuit for As long as the called subscriber does not hang up, theoperator will not withdraw the plug from jack JN. YI-Iereby relay COwill be held operated. With relay CO operated and relay LN released, acircuit will be completed via wire cato relay CH with effects as in theprevious example.

We claim:

1. In a telephone system, means including a plurality of seriallyrelated automatic switches including lboth backward and forwardselecting switches .operated to establish a connection `be-

